1. Field of the Invention
The present invention relates to a polysiloxane compound having a superior storage stability and more specifically it relates to a polysiloxane compound having an improved storage stability, which is useful as a surface treatment agent for silica or a compounding agent for a rubber composition.
The present invention also relates to a rubber compounding agent capable of improving the vulcanized physical properties of a vulcanizable silica formulated rubber composition, in particular the stress at tensile deformation, the wear resistance, and the tan .delta. balance and other physical properties and further relates to a rubber composition containing the same.
The present invention further relates to a vulcanizable silica formulated rubber composition having improved reactivity of the silica in the silica formulated rubber composition with the silane coupling agent, alkoxypolysiloxane, etc.
Note that, in the present specification, the "silica" means wet type silica and dry type silica having a nitrogen specific surface area of 50 to 400 m.sup.2 /g and the "vulcanization" includes cross-linking by, for example, a peroxide, in addition to normal vulcanization with sulfur.
2. Description of the Related Art
Rubber compositions containing various rubbers in which silica has been blended are known. For example, they are used as rubber compositions for tire treads with low heat generation and superior in wear resistance etc. However, while tire treads containing silica have a low rolling resistance and good grip on wet roads, phenomena such as increased viscosity of the unvulcanized formulation, delayed vulcanization, decreased kneading performance of the mixing, etc. arise in the process of manufacture of the tires, and therefore, there has been a problem of a reduction in the productivity. Various studies have been conducted in the past to solve these problems.
From this viewpoint, the present inventors previously proposed a rubber compounding agent comprising a polysiloxane and a silane coupling agent and a rubber composition in which the same was added (Japanese Patent Application No. 8-7663). When this was impregnated in the filler, weighing became easier, but there was the problem that when impregnated there was loss due to adsorption by the carbon etc.
In the past, rubber compositions comprised of various types of rubber containing silica have been used as rubber compositions for tire treads, but have had the defect of an inferior processability when unvulcanized. This is believed to be due to the silanol groups present in the structure. Therefore, the problem of the reduction in the processability has been solved by adding a polysiloxane having an acyloxysilyl group etc. to the rubber composition as a silica surface treatment agent to cause a reaction with the silanol groups and cover the silica surface. However, when synthesizing the above-mentioned polysiloxane, sometimes there are groups which do not become full alkoxylsilyl groups in the structure and remain as Si--H groups.
For example, among the above polysiloxanes, an alkoxy polysiloxane having the structure shown in Formulas (I) and (II) below is synthesized using an alkylhydrogen polysiloxane etc. and an alcohol or alkenyl alkoxysilane using chloroplatinic acid or other transition metal catalyst, but Si--H residual groups sometimes are present in its structure.
In general, a polysiloxane having Si--H groups easily reacts with water or alcohol to generate hydrogen gas in the presence of a platinum or other transition metal catalyst. Further, in a polysiloxane having a plurality of Si--H groups, gelation occurs during heating. Therefore, an alkoxypolysiloxane having Si--H residual groups gradually reacts with water or slightly remaining alcohol even at room temperature to generate hydrogen gas. Further, for example, it gels if stored near the temperature of heating at the time of synthesis of the polysiloxane, that is, 80.degree. C. This phenomenon becomes a problem in the safety and storage stability during storage or transport.
The above problem can be solved if the platinum or other transition metal catalyst is filtered out after the end of the reaction, but the removal of such a metal catalyst requires use of a special filter agent and the productivity is poor.
In silica formulated rubber compositions, various silane coupling agents, such as seen in Japanese Unexamined Patent Publication (Kokai) No. 6-248116, Japanese Examined Patent Publication (Kokoku) No. 6-76526, and Japanese Unexamined Patent Publication (Kokai) No. 8-59894, are used for the purpose of improving the modulus, breakage strength, elongation at break, wear resistance, and other vulcanized physical properties. Further, as disclosed in the specifications of Japanese Patent Application No. 7-223079, Japanese Patent Application No. 7-272859, and Japanese Patent Application No. 7-341540, etc. already filed by the present applicant, an alkoxypolysiloxane for improving the processability is used. However, the reaction between silica and the silane coupling agent or alkoxypolysiloxane is not that good, so a large amount of the silane coupling agent or alkoxypolysiloxane is required for obtaining the desired physical properties and performance.